The invention relates to the light source, and especially to the method for controlling a temperature of the light source used in the optical transmitter.
For realization of a wavelength division multiplexed (WDM, hereinafter) optical transmission system, it is very important to accurately control the wavelengths of signal lights outputted from an optical transmitter. The light source used in the WDM optical communication system comprises plural semiconductor laser diodes (LDs, hereinafter) serving as light emitting elements. Since the wavelength of a signal light emitted from the LD is closely related to a temperature of the LD, it is indispensable to precisely control the temperature of the LD in order to stabilize the wavelength of the signal light at a predetermined value. For example, the light source disclosed in Japanese Patent Kokai 9-191293, the LD is combined with a thermistor for detecting the temperature of the LD and a Peltier for cooling or heating the LD in accordance with a current supplied thereto, and supply of the driving current to the LD starts, when the temperature of the LD comes to be within the normal tolerance about the predetermined temperature. However, according to the aforementioned light source, the temperature of the LD deviates from the predetermined value to some extent because of heat generated by a driving current supplied the LD, and it is several seconds before the temperature of the LD, in other words, the wavelength of the signal light, comes to be within the normal tolerance. In order to remove the aforementioned disadvantage, it is extremely desirable to develop the light source, in which the temperature of the LD is controlled in condition that the driving current is being supplied to the LD and supply of the signal light to the outside is suppressed till the temperature of the LD comes to be within the normal tolerance.
It is an object of the invention to provide a light source, which comprises a single LD and forms a foundation of a large scale light source for a WDM optical transmission system.
It is a further object of the invention to provide a light source, which comprises a single LD, forms a foundation of a large scale light source for a WDM optical transmission system and is provided with means for improving an accuracy of control.
It is a still further object of the invention to provide a light source, which comprises plural LDs and is used for a WDM optical transmission system.
It is a yet further object of the invention to provide a light source, which comprises plural LDs, is used for a WDM optical transmission system and provided with means for improving an accuracy of control.
According to the first feature of the invention, a light source comprises:
a semiconductor laser diode (LD, hereinafter) module, which comprises a LD serving as a light-emitting element and means for detecting a temperature of the LD; and
means for suppressing supply of a light outputted from sad LD module to an outside till the temperature of the LD comes to be within a predetermined normal tolerance.
According to the second feature of the invention, a light source comprises:
a LD module, which comprises a LD serving as a light-emitting element and means for detecting a temperature of the LD,
means for detecting a wavelength of a light outputted from the LD module, and
means for suppressing supply of the light to an outside till the wavelength of the light comes to be within a predetermined normal tolerance.
According to the third feature of the invention, a light source comprises:
plural LD modules, each of which comprises a LD serving as a light-emitting element and means for detecting a temperature of the LD,
a multiplexer for multiplexing plural lights respectively outputted from the plural LD modules, and
means for suppressing supply of the multiplexed plural lights to an outside till temperatures of all the LDs come to be within predetermined normal tolerances.
According to the fourth feature of the invention, a light source comprises:
plural LD modules, each of which comprises a LD serving as a light-emitting element and means for detecting a temperature of the LD,
a multiplexer for multiplexing plural lights respectively outputted from the plural LD modules,
plural means for respectively detecting wavelengths of the plural lights, and
means for suppressing supply of the multiplexed plural lights to an outside till the wavelengths of all the plural lights come to be within predetermined normal tolerances.